This invention relates to an apparatus employing a dioptric or catoptric optical system for estimating the surface condition of a plate object to be tested. The term "surface condition" as used throughout this invention is intended to mean the degree of scratches, streaks, moisture, water droplets, water lines, water films, stains, and the like collected or left on the surface(s) of the plate object.
It is the current practice to estimate the surface condition of the plate object with the eye. Therefore, the estimation accuracy is dependent on the inspector's skill and is different from one inspector to another.